Carbon autonomy of reproductive shoots of Siberian alder (Alnus hirsuta var. sibirica)

Carbon autonomy of current-year shoots in flowering, and of current-year shoots plus 1-year-old shoots (1-year-old shoot system) in fruiting of Siberian alder (Alnus hirsuta var. sibirica) was investigated using a stable isotope of carbon, C-13. The current-year shoot and 1-year-old shoot systems were fed (CO2)-C-13 and the atom% excess of C-13 in flowers and fruits was determined. The majority of photosynthate allocated to flower buds was originally assimilated in the leaves of the flowering current-year shoots. Of all the current-year shoots on fruiting 1-year-old shoots, only those nearest to the fruits allocated the assimilated photosynthate to fruit maturation. These results indicate that the current-year shoots and 1-year-old shoot systems are carbon-autonomous units for producing flowers and maturing fruits, respectively.